[16.0][IMP] product_packaging_unece: cache UNECE code mapping

[sbejaoui]

add an ormcache based helper to map UNECE codes to packaging level

[OCA-git-bot]

Hi @jbaudoux,
some modules you are maintaining are being modified, check this out!

[sbejaoui]

cc/ @lmignon

[rrebollo]

@sbejaoui please prefix the PR title with "[16.0]"

[lmignon]

@sbejaoui when I read x_by_y I expect to receive a dictionary.... IMO the naming or the return value is not right....

get_packaging_level_ids(*unece_codes) -> list[int]: | get_packaging_level_ids_for_codes(*unece_codes) -> list[int]:

or

def get_packaging_level_id_by_unece_code(self, *unece_codes) -> dict[str, list[int]]:
    mapping = self._get_packaging_level_ids_by_unece_code()
    if len(unece_codes) == 1 and isinstance(unece_codes[0], (list, tuple, set)):
            unece_codes = unece_codes[0]
    return {code : mapping[code] for code in unece_codes if code in mapping}